Have you checked all the mechanical possibilities ?

Kink in liner?

Debris in liner?

Replace contact tube?

Solid connection to contactor?

When you hit the trigger are the rollers moving at all?

If the rollers are not turning, remove all tension and wire, and check again, are they turning now?

Hello brien, as Lawrence and ctacker have pointed out there are a number of things that can have an effect on wire feeding and other things related to machine operation. They are trying to provide you with things that should be checked before getting radical with a bunch of internal issues.
     When wire doesn't feed there are a host of things that can cause that problem, you need to go through the checklist similar to the one Lawrence posted. If the spool tensioning system is set-up too tightly that can cause the wire to stop feeding, if the wire has a cross wound into it due to improper handling of the spool before installing it onto the machine it can tie a knot in itself and stop wire from feeding. When the wire stops feeding it can either cause the feed rolls to stop turning completely or cause them to slip. I don't recall whether this particular machine has a thermal reset on it, but if it does it is possible that a birdnesting of the wire could have caused a short that tripped this reset or there could have been an overload of the feeder drive motor because you may have continued to depress the gun trigger and the drive motor hasn't been able to move so this may have tripped this reset. Getting back to gun and liner issues. A relatively quick way to tell if you have feed issues resulting from problems starting at the contact tip and working back to the spool tensioning mechanism. Release the feed roll tensioning arm so that it has no pressure on the wire, then take a pair of pliers and try pulling the wire through the system. It should pull with a slight bit of resistance but not of any noticeable amount. Next remove the contact tip and slide it off the end of the wire, if you notice a lot of pull when you are sliding the contact tip off that will be an indicator that the tip needs to be replaced. With the contact tip removed repeat the wire pulling scenario, if the wire still appears to have a lot of resistance, disconnect the gun from the wire feed block and slide it off of the wire, if you notice a lot of resistance when doing this it may indicate that the liner is possibly in need of cleaning or replacement or possibly had a kink or damage to it due to misuse or having something dropped on it. You've got basically two things left at this point, there is a wire guide that helps to line up the wire as it comes off of the spool and then aligns it with the drive rollers, sometimes this guide can get clogged or it can have tracks worn in it that will impede the wire feeding, loosen it and see how easily it slides on the wire, if it doesn't either clean it or replace it. Finally, you've got the spool tensioning mechanism, pull on the wire and see how much resistance you feel when doing this, if it's excessive you will need to adjust it so that it only has enough tension to stop the reel from overrunning when the trigger is released after the welding pass is completed. Beyond these items you will possibly need to look deeper into the machine, just keep in mind that these machines are not overly expensive to begin with and it may be a more economically feasibly move to buy a new one or a used one and keep yours for parts. Best regards, aevald

when you pull the trigger the you ear an internal click and the gas comes on but no wire feed? Have you checked operation without feeding wire? Diodes will affect the weld not the feed motor.

Output voltage is developed at the output studs and fed back to the control board. This welding output voltage is also used to power the drive motor. The output voltage that powers the drive motor is varied and controlled on the control board.

DC voltage at drive motor armature (wires 539 & 541) The voltage should be between 2 vdc and 10 vdc. The voltage will vary with the wire speed control setting. If motor armature voltage is NOT present then check wire speed pot and associated wires (208, 209, 203) for faulty connections. There are voltages to check at the control board plugs, but I do not feel confident to provide those, as further damge can be caused if done incorrectly.